All Questions
2,678 questions
96
votes
4
answers
13k
views
If Earth had rings?
If Earth had rings, would they center on the equator like Saturn's rings do on its equator?
- 1
89
votes
9
answers
222k
views
Why doesn't the Moon fall onto the Earth?
Why doesn't the Moon fall onto the Earth? For that matter, why doesn't anything rotating a larger body ever fall onto the larger body?
- 1,041
84
votes
4
answers
15k
views
Where does the extra kinetic energy come from in a gravitational slingshot?
I read in this answer in this site that the KE a free-falling ball acquires is not originated by the attracting body but that energy was actually stored in the ball when it had been lifted to the ...
- 851
78
votes
6
answers
10k
views
How can we see planets thousands of light years away but don't know if there are more planets in the solar system?
That is basically my question, it arose when I saw an article (here is the scientific paper, which should be free to read) saying two Caltech scientists might have found the 9th planet of the solar ...
- 1,768
78
votes
2
answers
10k
views
Can an atom orbit the Sun?
Is it possible for a molecule or atom to orbit a star (e.g. the Sun)? Or is there always too much outward force imparted by solar radiation compared to the inward force of gravitational attraction?
- 657
71
votes
5
answers
12k
views
Is there a small enough planet or asteroid you can orbit by jumping?
I just had this idea of orbiting a planet just by jumping and then flying upon it on its orbit kind of like superman. So,
Would it be theoretically possible or is there a chance of that small body to ...
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64
votes
15
answers
21k
views
Why do we say that the Earth moves around the Sun?
In history we are taught that the Catholic Church was wrong, because the Sun does not move around the Earth, instead the Earth moves around the Sun.
But then in physics we learn that movement is ...
- 1,387
61
votes
4
answers
9k
views
How far ahead can we predict solar and lunar eclipses?
The solar system is non-integrable and has chaos.
The sun-earth-moon three-body system might be chaotic.
So, how far into the future can we predict solar eclipses and/or lunar eclipses?
How about ...
- 4,152
60
votes
6
answers
19k
views
What symmetry causes the Runge-Lenz vector to be conserved?
Noether's theorem relates symmetries to conserved quantities. For a central potential $V \propto \frac{1}{r}$, the Laplace-Runge-Lenz vector is conserved. What is the symmetry associated with the ...
- 5,765
58
votes
4
answers
14k
views
What does the Moon's orbit around the Sun look like?
I'm curious as to what the Moon's orbit around the Sun looks like. If there's an answer, what's the intuition for it? Here are some things I'm assuming when trying to tackle this question:
The Moon's ...
- 761
55
votes
5
answers
100k
views
What did general relativity clarify about Mercury?
I frequently hear that Kepler, using his equations of orbital motion, could predict the orbits of all the planets to a high degree of accuracy -- except Mercury. I've heard that mercury's motion ...
- 5,091
53
votes
8
answers
8k
views
A planet with a square orbit?
To understand how gravity influence objects, time and space, I have been thinking of how a planets shape would change the orbits of its moons.
More specifically: can I design a planet whose moon move ...
- 1,153
50
votes
5
answers
31k
views
Is it possible to have a geostationary satellite over the poles?
My understanding of orbital mechanics is very limited, but as I understand geostationary satellite, they stay in place by having an orbital speed corresponding to the spot they're orbiting over.
So ...
- 627
49
votes
1
answer
5k
views
Why are our planets in the solar system all on the same disc/plane/layer? [duplicate]
I always see pictures of the solar system where our sun is in the middle and the planets surround the sun. All these planets move on orbits on the same layer. Why?
- 975
43
votes
5
answers
6k
views
If the gravitational force were inversely proportional to distance (rather than distance squared), will celestial bodies fall into each other?
If gravity was inversely proportional to distance, will the dynamics of celestial bodies be much different from our world? Will celestial bodies fall into each other?
- 589
43
votes
2
answers
7k
views
Is our solar system really that odd?
I have been learning about the solar system from popular science shows. In these shows they suggest that, after having seeing around 2500 other solar systems, astronomers have concluded that our ...
- 1,430
41
votes
7
answers
15k
views
Why don't we feel the subtle speed change of Earth's elliptical orbit?
Earth's orbit is a slight ellipse, so to conserve momentum its speed increases when it is closest to the Sun. If the speed changes there is an acceleration. If there is an acceleration there is a ...
- 2,908
41
votes
1
answer
5k
views
Why is the period of a geostationary satellite not exactly 1440 minutes?
When reading about Astra satellites on Wikipedia (https://en.wikipedia.org/wiki/Astra_1KR), I saw that the period of the Astra 1KR satellite, positioned at 19.2° E, is 1,436.1 minutes (source: NORAD ...
- 471
41
votes
6
answers
91k
views
Why don't planets have Circular orbits?
This might be a completely wrong question, but this is bothering me since many days ago. Given the mass (Sun) curves the space around it, gravitation is the result of such curved space (Correct me if ...
- 545
39
votes
6
answers
10k
views
Why aren't satellites disintegrated even though they orbit earth within earth's Roche Limits?
I was wondering about the Roche limit and its effects on satellites.
Why aren't artificial satellites ripped apart by gravitational tidal forces of the earth?
I think it's due to the satellites being ...
- 741
36
votes
3
answers
23k
views
Might a planet perform figure-8 orbits around two stars?
Might a planet perform figure-8 orbits around two stars?
I'm thinking that if the two stars were equal mass (and not orbiting each other) then a planet that were to go right between them would ...
- 4,543
35
votes
6
answers
14k
views
Could there be a star orbiting around a planet?
I wonder if there ever could be a star (really small) which may orbit around a planet (really big)?
- 351
35
votes
5
answers
5k
views
Can the Schrodinger equation describe planetary motion? [duplicate]
I was asked on an exam whether the Schrodinger equation can be used to describe planetary motion and my answer was "No, because the solutions are wavefunctions which give probabilities but everything ...
- 909
35
votes
5
answers
11k
views
How do you calculate the anomalous precession of Mercury?
One of the three classic tests of general relativity is the calculation of the precession of the perihelion of Mercury's orbit.
This precession rate had been precisely measured using data collected ...
- 77.3k
35
votes
5
answers
4k
views
Why is argon a noble gas but not, say, beryllium or palladium?
Why is argon a noble gas given that the 3d subshell is still empty?
More generally, why is it that the filling of a p sub-shell makes an element noble rather than s, d, or f sub-shells, or completed n-...
- 3,576
34
votes
7
answers
3k
views
Cause of weightlessness [duplicate]
I'm a first year engineering student who is new to physics, so I apologize if my question is stupid. But in our statics course we are using the book "Engineering mechanics: statics" by R.C. Hibbeler ...
- 359
33
votes
3
answers
7k
views
Is there a maximum distance from a planet that a moon can orbit?
Given a planet that orbits a star, and a moon that orbits that planet, is it possible to define a maximum orbital radius of that moon, beyond which the moon would no longer orbit the planet, but the ...
- 432
33
votes
3
answers
8k
views
If we threw a baseball from the ISS, could we deorbit the ball?
Clearly this is a hypothetical question.
Say we bring a star baseball player into NASA, prep them appropriately for a mission in space, and fly them up to the International Space Station. They go on ...
- 453
33
votes
3
answers
6k
views
Why do the planets' orbital distances fall on an exponential curve?
Background: I was recently reading a book on the planets to my son and I noticed a pattern in the distributions of the planets. The planets' distances roughly follow an exponential distribution.
...
- 708
32
votes
2
answers
5k
views
Free fall ellipse or parabola?
Herbert Spencer somewhere says that the parabola of a ballistic object is actually a portion of an ellipse that is indistinguishable from a parabola--is that true? It would seem plausible since ...
- 447
31
votes
1
answer
3k
views
Why does it take so long to get to the ISS?
I don't understand why when first launched Space X's Dragon capsule had to orbit the Earth many times in order to match up with the ISS? Was this purely to match it's speed, or to get closer (as in ...
- 6,987
31
votes
5
answers
7k
views
Why doesn't dark matter affect planetary motion?
If the universe is made up of ~95% dark matter, and it interacts only gravitationally then why didn't Newton and Kepler discover it before ? Why does it show itself only in the radial velocity profile ...
- 311
30
votes
5
answers
5k
views
Do planets orbiting stars emit gravitational waves?
I have heard it said that charged planets could not orbit a massless (low mass) oppositely-charged star based on electromagnetic attraction the same way they can with gravitational attraction, because ...
- 630
30
votes
6
answers
14k
views
Why are the orbits of planets in the Solar System nearly circular?
Except for Mercury, the planets in the Solar System have very small eccentricities.
Is this property special to the Solar System? Wikipedia states:
Most exoplanets with orbital periods of 20 days ...
- 53.7k
29
votes
5
answers
12k
views
Build a ring around Earth, then remove the supports
What would happen if we decided to build a giant ring that managed to wrap around the whole world, end to end that was supported with pillars all along the ring and then the supports all suddenly ...
- 439
29
votes
4
answers
10k
views
Why doesn't the Moon disrupt the orbits of geostationary satellites?
If a passing star can jostle comets in the Oort Cloud, why doesn't the Moon disrupt the orbits of high-flying satellites?
Or does it? Maybe the satellites need periodic course corrections?
- 401
29
votes
4
answers
7k
views
Are planets actually moving in elliptical orbits around the Sun or do they move in circular orbits around their center of mass?
In every derivation of Kepler's Laws that I have seen, we assume that the sun is stationary. However, in other places I have read that celestial bodies move about their barycentre (center of mass).
So ...
29
votes
5
answers
16k
views
Gravity in other than 3 spatial dimensions and stable orbits
I have heard from here that stable orbits (ones that require a large amount of force to push it significantly out of it's elliptical path) can only exist in a three spatial dimensions because gravity ...
- 485
29
votes
3
answers
10k
views
Are tidal power plants slowing down Earth's rotation?
Are tidal power plants slowing down Earth's rotation to the speed of the orbiting moon? (1 rotation per 28 cca days)
Are they vice versa increasing the speed of moon orbiting by generating some ...
- 1,938
28
votes
2
answers
4k
views
If the 3-Body force problem hasn't been solved, how do rocket scientists plan orbits of spacecraft?
What methods would they use to predict what would happen in a situation when a probe is being acted upon by the gravity of two stars, say?
- 423
27
votes
3
answers
5k
views
What causes our Sun to oscillate around its mean Galactic orbit?
According to this answer on Astronomy.SE,
The Sun executes oscillations around its mean orbit in the Galaxy, periodically crossing the Galactic plane. I borrowed this illustration (not to scale!) ...
- 5,114
26
votes
13
answers
5k
views
Escape velocity - Won't the orbital path just become larger with higher initial velocity?
Escape velocity is the minimum speed needed for an object to escape from the gravitational influence of a massive body. However, gravity has infinite range. Object $A$ is always getting pulled by the ...
- 377
26
votes
10
answers
9k
views
Does gravity sometimes get transmitted faster than the speed of light?
Consider Earth moving around the Sun. Is the force of gravity exerted by Earth onto the Sun directed towards the point where Earth is "right now", or towards the point where Earth was 8 minutes ago (...
- 979
26
votes
9
answers
28k
views
Why are orbits elliptical? [duplicate]
Almost all of the orbits of planets and other celestial bodies are elliptical, not circular.
Is this due to gravitational pull by other nearby massive bodies?
If this was the case a two body system ...
- 1,394
26
votes
7
answers
87k
views
Gravity on the International Space Station
We created a table in my physics class which contained the strength of gravity on different planet and objects in space. At altitude 0 (Earth), the gravitational strength is 100%. On the Moon at ...
- 363
26
votes
4
answers
3k
views
How do the “hot Jupiter” planets get so close to their host star?
Many of the extrasolar planets to date are Jovian sized planets that orbit very very close to their parent star. Traditional planetary formation models say that it is extremely unlikely (if not ...
- 6,467
25
votes
3
answers
8k
views
Why don't we put satellites into an orbit where there is (almost) no time dilation/contraction compared to Earth's surface?
Consider:
On this image, if I understand correctly, the time dilation diagram is shown depending on the height for circular orbits. First in low orbit, time slows down relative to the surface due to ...
25
votes
7
answers
6k
views
Why are there so many objects perfectly orbiting each other? Isn't it infinitely more likely that two random objects crash/fly apart?
If, in free space, I throw two objects towards each other, they can either miss each other and fly apart (if the velocity is enough and there's not enough gravitational attraction between them), or ...
- 1,092
24
votes
4
answers
4k
views
For a spacecraft orbiting a planet, orbital speed is inversely proportional to orbit radius. But speed must be increased to increase orbit radius?
For a spacecraft in orbit with radius $r$ with speed $v$ around a planet, centripetal force $F_C$ is provided by gravity:
$$\frac{GmM}{r^2}=\frac{mv^2}{r},$$
which simplifies to
$$\frac{GM}{r}=v^2.$$
...
- 383
24
votes
4
answers
6k
views
Significance of the second focus in elliptical orbits
1.In classical mechanics, using Newton's laws, the ellipticity of orbits is derived. It is also said that the center of mass is at one of the foci.
2.Each body will orbit the center of the mass of ...
- 1,447